Mixed potential sensors for the detection of hydrocarbons and carbon-monoxide have been previously studied at Los Alamos National Laboratory (LANL). The LANL sensors have a unique design incorporating dense ceramic-pellet/metal-wire electrodes and porous electrolytes. When these sensors are exposed to various gases, in addition to their mixed-potential response, their resistance changes. This change in resistance is probably associated with the oxygen reduction reaction at the electrode/electrolyte interface and can be used to yield a total NOx response. The NOx sensors are operated in a current bias mode where the voltage response is related to the total NOx concentration. (c) 2006 The Electrochemical Society.